Daemon User Interface
Every program needs a way to communicate with its users. It needs a way for users to specify their wishes, and it needs a way to let them know the outcome of that wish. Since a daemon is not attached to a terminal and usually has no graphical display, we can communicate with it using one of the following means:
Environment Variables
Command Line Arguments
Any form of IPC (Inter Process Communication) mechanism
Pipes
Sockets
Others Mechanisms